fix(core): skip media preloader activation in render mode

mediaPreloader.refresh() was called unconditionally, setting lazy=true
for compositions with ≥6 clips even in render mode. player.seek then
called preloadAroundTime() which evicted clips via src clearing,
destroying buffered data needed for frame-accurate capture.

Skip refresh() when __HF_EXPORT_RENDER_SEEK_CONFIG is set so isLazy()
stays false and the preloader is completely inert during renders.

packages/core/src/runtime/init.ts

@@ -1243,7 +1243,7 @@ export function initSandboxRuntimeModular(): void {
       mediaEl.addEventListener("durationchange", scheduleMetadataDurationHydration);
     }
 
-    if (newElementsBound) {
+    if (newElementsBound && !isRenderMode) {
       mediaPreloader.refresh();
     }